The present invention relates generally to a Hybrid Electric Vehicle (HEV), and specifically to an HEV system controller to monitor component conditions such as temperature and control the cooling system fan speed.
The need to reduce fossil fuel consumption by and emissions from automobiles and other vehicles powered by an Internal Combustion Engine (ICE) is well known. Vehicles powered by electric motors attempt to address these needs. However, electric vehicles have limited range, limited power capabilities and need substantial time to recharge their batteries. An alternative solution is to combine both an ICE and electric traction motor into one vehicle. Such vehicles are typically called Hybrid Electric Vehicles (IEVs). See generally, U.S. Pat. No. 5,343,970 (Severinsky).
The HEV is described in a variety of configurations. Many HEV patents disclose systems in which an operator is required to select between electric and internal combustion operation. In other configurations, the electric motor drives one set of wheels and the ICE drives a different set.
Other, more useful, configurations have developed. For example, a Series Hybrid Electric Vehicle (SHEV) configuration is a vehicle with an engine (most typically an ICE) connected to an electric motor called a generator. The generator, in turn, provides electricity to a battery and another motor, called a traction motor. In the SHEV, the traction motor is the sole source of wheel torque. There is no mechanical connection between the engine and the drive wheels. A Parallel Hybrid Electrical Vehicle (PHEV) configuration has an engine (most typically an ICE) and an electric motor that together provide the necessary wheel torque to drive the vehicle. Additionally, in the PHEV configuration, the motor can be used as a generator to charge the battery from the power produced by the ICE.
A Parallel/Series Hybrid Electric Vehicle (PSHEV) has characteristics of both PHEV and SHEV configurations and is typically known as a xe2x80x9cpowersplitxe2x80x9d configuration. In the PSHEV, the ICE is mechanically coupled to two electric motors in a planetary gearset transaxle. A first electric motor, the generator, is connected to a sun gear. The ICE is connected to a carrier. A second electric motor, a traction motor, is connected to a ring (output) gear via additional gearing in a transaxle. Engine torque powers the generator to charge the battery. The generator can also contribute to the necessary wheel (output shaft) torque. The traction motor is used to contribute wheel torque and to recover braking energy to charge the battery if a regenerative braking system is used.
The desirability of combining an ICE with an electric motor is clear. The ICE""s fuel consumption and emissions are reduced with no appreciable loss of vehicle performance or range. Nevertheless, there remains a substantial opportunity to develop ways to optimize HEV operation.
One such area of development is in the HEV""s cooling system. In conventional vehicles, the cooling system has a variety of components that require cooling by a fluid cooling system, radiator and fan. Fluid cooled components typically include the engine and transmission. A fluid coolant circulates through a closed cooling loop, passes through each component to absorb heat, and then passes through the radiator. The radiator exposes the coolant to the fan""s airflow and releases the heat. A controller monitors engine and transmission temperatures and adjusts fan speed to maintain acceptable coolant temperature for that cooling loop. In addition to the fluid cooled components, the air conditioning (A/C) condenser requires cooling from airflow, that comes from the fan(s) to keep the A/C compressor head pressures at acceptable levels.
HEVs contain new components not included in conventional cooling systems. Therefore, a new cooling system must be devised to maintain HEV component function, efficiency, and productivity.
Accordingly, the present invention provides a method and system to cool HEV components.
Controlling HEV component temperatures below calibratable thresholds ensures not only functionality of vehicle components but also operational efficiency. The present invention identifies components requiring cooling. These components are both related to the ICE and unique to the HEV as part of the electric drive system. The HEV electric drive system can include a DC/DC converter, transmission, inverter, generator motor, and traction motor. The present invention combines both component groups into one cooling system, thereby avoiding redundancy while maintaining efficiency.
A pump maintains system component temperature by moving coolant through the closed cooling loop. As the coolant passes through each component, it absorbs component heat. The coolant then passes through a radiator where the coolant vents heat to the outside when exposed to fan airflow.
A controller monitors component temperatures and regulates the fan speed. Component temperatures are determined by measuring actual component temperatures such as cylinder head temperature, transmission/transaxle oil temperature, inverter die temperature, and motor winding temperatures or by measuring the coolant temperature. The controller compares component temperatures with calibratable thresholds to determine whether the fan should be operating and, if so, at what speed the fan should be operating.